Poly(ethylene glycol) is commonly used as a polar polymer for immobilization on a substrate's surface. These substrates are used as stationary phases for chromatographic separations and as extraction sorbents. However, poly(ethylene glycol) has insufficient polarity for absorption and analysis of many highly polar analytes. Immobilization of polar polymers, including poly(ethylene glycol), on a substrate's surface is considered a challenge to surface chemists. In a conventional coating process, a thin coating of the polymer is deposited on the substrate's surface, followed by free-radical cross-linking reaction that forms a mesh-like network to anchor the coating to the surface. Bound poly(ethylene glycol) behaves like a pseudo-liquid that retains target analytes via dissolution. The dissolution of analytes in a highly viscous solid can be a slow process that requires long extraction time to reach equilibrium. Absent chemical linkage between the polymer film and the substrate surface, the sorbent coating is vulnerable to being washed out by organic solvents nor can the coated substrate be exposed to high temperature; as when heated for thermal desorption after an analyte extraction or when employed as a chromatographic stationary phase. Incorporation of poly(ethylene glycol) polymer in the sol-gel matrix (sol-gel coating technology) improves solvent resistance and thermal stability of the composite material.
Nevertheless, the limited polarity of poly(ethylene glycol) remains a problem when employed to target very highly polar analytes. To the end a simple and environmental friendly approach of immobilization of highly polar molecules to a metal oxide network for use as superpolar stationary phase and/or extraction sorbent is desirable. Such a composition can have properties derived from being a sol-gel inorganic/hybrid organic-inorganic polymeric network that can be formulated to display adjustable porosity, tunable selectivity, high thermal stability, solvent stability, and wide pH stability.